In recent years, data volumes processed by computer systems have been increasing. Therefore, in a large-scale computer system, a distributed storage system for distributing and storing data into multiple storage nodes has been used.
In the meantime, as the computer system and the storage system grow in size, the power consumption of the computer system is becoming a problem.
Therefore, attempts to reduce the power requirements of the storage system have been made, such as to change the rotation speed of a disk drive or to turn a disk off. An example of the technology using such a mechanism is disclosed in Patent Literature (PTL) 1. In a method disclosed in PTL 1, the disk drive is turned off when no access to the disk drive is expected to reduce the power consumption of the system.
Further, a system for reallocating data in a distributed storage system by using non-access probability calculated based on statistics information on accesses to distributed storage nodes is disclosed in Patent Literature (PTL) 2. In the system disclosed in PTL 2, data allocation is so made that an expected value of a non-access period will become high and hence the period of keeping each disk node in a power saving mode can be longer.
In addition, a computer system for distributing I/O (Input/Output) load properly is disclosed in Patent Literature (PTL) 3. In the computer system disclosed in PTL 3, an average frequency of I/O accesses to each integrated device is calculated as an estimate of the I/O access frequency.